The invention relates to a device for processing a continuously running web material. Typically, the device has a machine frame, an ultrasonic generator unit that has a sonotrode which is movably mounted to the machine frame, a counter tool that lies opposite the sonotrode and which is supported on the machine frame, some means for passing the web material through the gap between the sonotrode and the counter tool, and a drive, activated by a fluid pressure medium, for pressing the sonotrode against the counter tool.
The processing tasks to which such hardware is directed include, for example, reinforcement of a nonwoven made up of thermoplastic fibers, by melting the fibers in certain spots. In this connection, the sonotrode rests on the nonwoven with a certain force, in order to ensure that the ultrasound energy is effectively introduced into the nonwoven. On the back, the nonwoven rests on the counter tool, which is structured as a counter roller, for example.
In order to achieve an optimum processing effect that remains uniform over the surface of the material web, very precise control over the distance and thus the force between the sonotrode and the counter tool (or the sheath surface of the relief affixed to it, if present) is required.
It is usual to press sonotrodes, i.e. the material web that is located between them, against the counter tool with a constant force, using pneumatic cylinders. However, the sonotrode is not supported in rigid manner in this connection, but rather via a force cushion that acts like a spring. To a certain extent, a hydraulic contact pressure system is also resilient.
Due to irregularities in the position of the nonwoven, and possibly also due to the relief pattern applied to the counter tool, i.e. the counter roller, the sonotrode may vibrate perpendicularly to the counter tool. This vibration movement has the result that the processing effect varies due to the rhythm of the vibration frequency. In other words, the nonwoven web is periodically reinforced less at one point of its length, and more at another, or might even be cut. Such irregularities are, of course, very undesirable.
The present invention is directed to the task of further developing a device of this type such that it has a more uniform processing effect. A damping device is provided to ensure that the vibrations excited by the web or the counter tool are damped to such an extent that they are no longer noticeable in the processing effect.
One such damping device is a piston/cylinder combination, attached to the sonotrode through one of the elements and to the machine frame at the other of the elements. The fluid located between the surfaces of the elements mentioned undergoes strong shear when the surfaces move relative to one another, and exerts its damping effect by internal fluid friction. For example, an arrangement of plates that are parallel to one another and lie opposite one another at a slight distance, similar to an electrical plate capacitor, is possible.
In the preferred embodiment, however, the damping device is structured as a piston/cylinder unit, where the fluid is located between the outside circumference of the piston and the inside circumference of the cylinder.
Damping devices as such are discussed in the book xe2x80x9cGerxc3xa4tekonstruktionxe2x80x9d(Device Design), edited by W. Krause, Dr. is Alfred Hxc3xcthig Verlag, Heidelberg (1987), pages 326-328. The book xe2x80x9cxc3x96lhydraulikxe2x80x9d (Oil Hydraulics) by G. Bauer Verlag B. G. Teubner, Stuttgart (1992), pages 150/151, particularly FIG. 86, shows a spindle valve that has a damping piston to prevent fluttering of the valve body, but here the damping effect comes about primarily by an overflow process resulting from a reduced cross-section.
The primary fluid that can be used is an oil, the viscosity of which is suitably selected.
The distance between the surfaces, i.e. the radial distance between the outside circumference of the piston and the inside circumference of the cylinder also depends on the viscosity. This distance can vary approximately within a range of 2 to 50 xcexcm, where the selection depends on the size of the damping device, the desired damping effect, and, of course, on the viscosity of the oil being used, in an individual case.
According to one embodiment the damping device and the drive which is used to set the sonotrode against the counter tool or to lift it from the latter are combined in a module.
This can be accomplished, for example, by a dual-action piston/cylinder unit.
When oil is used as a fluid pressure medium, the piston can be cylindrical, without a piston ring where the piston has sufficiently small play in its cylinder so that the contact pressure movement is possible when force is exerted, but at the same time, sufficiently great play so that the fluid damping effect is possible. If, however, air is used as the fluid pressure medium for the contact pressure movement, the piston should have piston rings. Air is not suitable for achieving a sufficiently great damping effect at low vibration amplitudes. Therefore a liquid is provided as the damping medium in the space between the piston rings, which can be supplied to the interstitial space via a special feed line.